I recently made an unexpected finding that the cerebellum of the frog tadpole is so immature that the external granular layer is altogether absent and that, in the case of the bullfrog tadpole, it remains in this condition for two or three years and undergoes maturation at the time of metamorphosis. I later found that the tadpole cerebellum can be readily induced to undergo precocious maturation by thyroid hormone treatment. This grant proposal is designed to undertake a detailed study of the morphological changes that take place during both normal and thyroid-induced metamorphosis. The methodology will include radioautography, Golgi silver impregnation and electron microscopy. BIBLIOGRAPHIC REFERENCES: Gona, A.G., 1975. Radioautographic studies of metamorphic changes in the frog cerebellum. Anat. Rec., 181, 363. Gona, A.G., 1975. Golgi studies of cerebellar maturation in frog tadpoles. Brain Res., (In press).